1. Field of the Invention
The invention relates to semisolid polymerizable unsaturated polyester resin syrup compositions, to methods of making such compositions, to methods of curing such compositions and to the thermoset products obtained by polymerizing such compositions.
2. Description of the Prior Art
Unsaturated polyester resin syrups have been employed in the production of a wide variety of products. See Polyester Resins and Their Applications, Bjorksten et al, Reinhold Publishing Company, New York, 1960 (Fourth Printing). The unsaturated polyester resin syrups customarily are reinforced with fibrous fillers such as glass fibers and also are extended with inert particulate fillers such as wood flour, silica, ground glass, clay, calcium carbonate, and the like. Typical end products include flat and profiled building sheets, automobile components, furniture, plumbing fixtures, ductwork, boats, electrical housing components, electrical circuit boards and the like.
U.S. Pat. No. 3,978,018 describes compositions containing unsaturated polyester resin syrups and aqueous alkali-stabilized colloidal silica which thicken and remain polymerizable until exposed to polymerizing conditions. In one embodiment of the prior process, the unsaturated polyester resin syrup and the aqueous alkali-stabilized colloidal silica are combined and polymerized concurrently. In a further embodiment of the earlier invention, the aqueous alkali-stabilized colloidal silica and unsaturated polyester resin syrup are combined, with or without fillers, and allowed to thicken for subsequent reuse. One typical reuse is in the form of molding powders where the thickened mixtures are ground, chopped or pulverized for subsequent molding.
One of the shortcomings of the polymerizable mixtures is that the requirement for thickening establishes some restraints on the ratio of aqueous alkali-stabilized colloidal silica and unsaturated polyester resin syrup which may be combined for developing specific thickening characteristics. The act of mixing the unsaturated polyester resin syrup with the aqueous alkali-stabilized colloidal silica brings about changes in the composition of both the colloidal silica and the unsaturated polyester resin syrup. Specifically the colloidal silica becomes at least partially gelled. The unsaturated polyester resin syrup has some of its carboxylic end groups converted to carboxylate salts by the alkali which serves as stabilized in the colloidal silica. The resulting material is not an emulsion but instead appears to be a mixture of the ingredients.
The mixture may harden rapidly or slowly to a final consistency depending upon the ratios of aqueous alkali-stabilized colloidal silica and unsaturated polyester resin syrup. There is a need for regulating the thickening rate and final consistency of such mixtures. Rapid thickening is particularly desirable when manufacturing sheet molding compounds, bulk molding compounds or molding powders.
In a copending application Ser. No. 655,012, filed Feb. 4, 1976 (a continuation-in-part of Ser. No. 597,673, filed June 21, 1975, abandoned, which in turn was a continuation-in-part of Ser. No. 544,966, filed Jan. 29, 1975, which in turn was a continuation-in-part of Ser. No. 460,489, filed Apr. 12, 1974, abandoned), I have described the use of calcium sulfate hemihydrate in molding compositions as a means for controlling the thickening of polymerizable compositions including unsaturated polyester resin syrup and aqueous sodium silicate.